Apparatus for making a metal print drum

ABSTRACT

Apparatus and method for making a metal print drum by isostatic compression of powdered metal using a thin compressible cylindrical character sleeve having relatively deep character depressions in its inner surface. The deep character depressions isostatically allow for the formation of sharply raised print characters on the outer surface of the metal print drum located between the character sleeve and a centrally positioned expandable bag. The expandable bag expands outwardly to compress powdered metal against the inner surface of the character sleeve under a high pressure. After compression of the powdered metal, the metal print drum and character sleeve together are removed from the center of a support ring which was used to support the character sleeve during isostatic compression and the character sleeve is cut from the metal print drum. The metal print drum is then sintered at a high temperature to harden it.

Unite States Schwarzkopf 451 N 25, 1975 1 APPARATUS FOR MAKING A METAL 3,594,877 7/1971 Suda et 111.... 425/405 1-1 PRINT DRUM $619,446 11/1971 Nauta 425/D1G. 44

[75] Inventor: Peter Schwarzkopf, Westminster, Primary Examiner ji Howard Flint, Jr-

Cahf' Attorney, Agent, or FirmRobert R. Hubbard [73] Assignee: Peter Schwartzkopf, Westminister.

Calif. [57] ABSTRACT [22] Filed: May 9, 1973 Apparatus and method for making a metal print drum by isostatic compression of owdered metal usin a [21] Appl' 358560 thin compressible cylindrical character sleeve hafing relatively deep character depressions in its inner sur- [52] US. Cl. 425/78; 425/405 11; 425/1316, 44 face. The deep character depressions isostatically [51] Int. Cl. B30B 5/02; B308 1 1/00 ll w for the formation of sharply raised print charac- [58] Field of Search. 425/405 1-1, DIG. 44, DIG. 29, ters on the outer surface of the metal print drum 10- 425/78, DIG, 124 cated between the character sleeve and a centrally positioned expandable bag. The expandable bag expands [56] References Cited outwardly to compress powdered metal against the UNITED STATES PATENTS inner surface of the character sleeve under a high 2,091,973 9/1937 Fessler et al 425/405 H x pressure After compresson of the powdered metal 2558.823 7/1951 Crowley et al 425/405 11 x the metal drum and Character are 2,582,922 1/1952 Crowley et al 425 405 11 X removed from the center of a support mg whlch was 2,714,226 8/1955 Axelrad 425/1310. 44 used to pp the Character Sleeve during isostatic 2,871,541 2/1959 James 425/D1G 124 compression and the character sleeve is cut from the 2,965,946 12/1960 Sweet et a1. 425/D1G. 44 metal print drum. The metal print drum is then sin- 3,034,l91 5/1962 Schafer 425/405 H X tered at a high temperature to harden i[ 3,477,096 11/1969 Bowles et al.. 425/405 H 3,561,079 2/1971 Anderson 425/405 1-1 X 4 Claims 5 Drawing Figures US. Patent Nov.2 5, 1975 Sheet 1 of3 2 3,922,127

FIGURE l US. Patent Nov. 25, 1975 Sheet 2 of 3 FIGURE 2 PRESS 62 i j 16v 5 3 3 :q-h-n. d-P. @g I a Q: #68 16 2; a i 40 (66 M ELTED WATER PLASTIC coouNe INJECTOR FIGURE 3 US. Patfint Nov.25, 1975 Sheet30f3 3,922,127

FIGURE 4 FIGURE 5 APPARATUS FOR MAKING A METAL PRINT DRUM BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the isostatic compression of powdered metal against a cylindrical plastic character sleeve with a centrally positioned expandable bag to form a metal print drum.

2. Discussion of the Prior Art In U.S. Pat. No. 2,847,708 H. J. Hamjian uses an expandable bag at the interior of a rigid cylindrical ring to isostatically compress powdered metal against the inner surface of a metal ring. I-Iamjian thus forms a hollow cylindrical metal article which has a smooth outer surface. Hamjian does not suggest apparatus and method to form raised characters on the outer surface of a hollow cylindrical metal article.

It is an object of the present invention to provide apparatus for making a hollow cylindrical metal print drum having sharply raised characters on its outer surface by isostatic compression of a powdered metal.

Further in the prior art, a metal printdrum has been formed from a smooth metal cylinder by first etching portions of the metal cylinder to form a pattern of characters on the metal cylinder and then increasing the height of the characters on the metal cylinder by rolling the metal cylinder against a second metal cylinder which has character depressions formed into its outer surface. The apparatus required to make such a print drum wears quickly and is difficult to make, and the process of making such a print drum is slow and expensive.

SUMMARY OF THE INVENTION In the present invention a compressible cylindrical character sleeve having character depressions on its inner surface is positioned within a support ring, which together circumscribe. an expandable bag. Powdered metal is placed between the expandable bag and the character sleeve and the expandable bag is pressurized to cause it to expand under a high pressure in order to form a hollow cylindrical metal print drum which has sharply raised print characters on its outer surface. The character sleeve is made of a material such as polyurethane which may be cut from the hollow metal print drum after the hollow metal print drum and character sleeve are removed from the support ring. A metal mounting core is then placed within the hollow metal print drum and the combination is sintered. The character sleeve is used as a part of an isostatic compression apparatus and method for makinga hollow metal print drum. The character sleeve is made relatively thin compared to the thickness of a finished hollow metal print drum and the character depressions in the inner surface of the character sleeve are made to a depth which is a large percentage of the total thickness of the character sleeve to tightly compress the powdered metal of the character portions of the metal print drum as the powdered metal is compressed against the character sleeve. The powdered metal which makes up the tops of the raised print characters of the print drum moves only a small distance during the isostatic compression process since the character depression areas of the character sleeve are very thin, with the result that the strength of the metal which makes up the tops of the raised characters is great. The use of a character sleeve which has 2 deep character depressions allows for the fabrication of a metal print drum whose metal characters therefore have a long printing life.

The metal print drum formed by the presently disclosed method and apparatus uses an easily formed plastic character sleeve, and the time required to form a metal print drum by the presently disclosed method is short since the time required to compress powdered metal and sinter it is short. The powdered metal is compacted under a very high pressure and the resultant metal print drum will give a long period of service. The present method does not require machining to form the outer surface of a metal print drum.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a plan view of isostatic compression apparatus used to make a metal print drum.

FIG. 2 is an elevational view of a compressible character sleeve used in the apparatus of FIG. 1 to make a metal print drum.

FIG. 3 is a plan view of an injection mold used to make the compressible character sleeve of FIG. 2.

FIG. 4 is a sectional view of the apparatus of FIG. 1.

FIG. 5 is an elevational view of a metal print drum which was made in the apparatus of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the reference numerals of the drawings, the apparatus and method for making a metal print drum are described below.

A conventional hydraulic press 12 has an upper vertically aligned ram 14 and a lower vertically aligned ram 16. A removable mold 18 is positioned between the two rams l6 and 18 within a metal enclosure 20 which is made of steel. The upper ram 14 is movable downward to apply pressure to hold the mold 18 together during isostatic compaction and the lower ram 16 is movable upward to push the removable mold 18 out of the metal enclosure 20 after isostatic compaction. The bottom ram 16 has a bore hole 22 adapted to align with a hole 24 in a support cylinder 26 which may be made from beryllium copper. The upper surface 28 of the ram 16 and lower end of the support cylinder 26 have matching conical surfaces. A conventioanl O-ring seal 30 is formed partially into the surface 28 of lower ram 16 to provide a pressure seal between the ram 16 and support cylinder 26.

The removable mold 18 has a support cylinder 26, an expandable bag 32 over the upper end of the support cylinder 26, a sealing ring 34 over a lip 36 of the expandable bag 32 and surrounding the lower end of the bag 32 and support cylinder 26, a support ring 38 resting on the sealing ring 34 and surrounding the central portion of the bag 32 and support cylinder 26 and further supporting a compressible character sleeve 40 on its inner surface, and a top ring 42 resting on the support ring 38 and forming a compression cavity 44. The support cylinder 26 and expandable bag 32 are located approximately one-quarter inch from the character sleeve 40. The expandable bag 32 can be made of a material such as polyvinyl chloride. The rep ring 42 and sealing ring 34 position the character sleeve 40 within the support ring 38. The rings 42, 38 and 34 have an interleaving construction to provide a closed compression cavity 44 from which powdered metal 46 cannot escape during isostatic compression. The rings 42, 38 and 34 can be made of standard 4340 steel. The cylindrical support 26 has a network of internal bore holes 47 for conveying pressurized glycerine 48 into the bag 32. The lip 36 of the expandable bag 32 makes a tight seal against glycerine leakage when sealing ring 34 and support cylinder 26 are pushing on it. The character sleeve 40 is made of a compressible material such as polyurethane and has character depressions 49 formed on its inner surface. The polyurethane material of the character sleeve 40 can have glass fibers in it to prevent the character depressions 49 from moving vertically during isostatic compression. This glass fiber reinforcement of the character sleeve assures that the characters on the finished drum (see FIG. 5) have the proper inter-character spacing along a line of characters which is parallel to the drum axis.

The lower ram 16 is on a base 50 through which bore 22 passes. A pipe 51 is connected to the base 50 at the bore 22 and a hydraulic pressure multiplier 52 is connected to the pipe 51. A second pipe 53 connects the multiplier 52 to a hydraulic pump 54.

In order to form a metal print drum 55 in the removable mold 18, the lower ram 16 is raised to push the removable mold out of the metal enclosure 20 and the mold 18 is removed from between rams 14 and 16. The top ring 42 is then removed from the removable mold 18 and a measured charge of powdered metal 46 is placed in the compression cavity 44. The opened mold 18 is then placed on a vibrating table to vibrate the powdered metal 46 firmly into the compression cavity 44 and then the top ring 42 of the mold 18 is placed on support ring 38. The mold 18 is then placed on the lower ram 16 and the upper ram 14 is placed against the mold 18 and the two rams are lowered to lower the mold 18 into metal enclosure 20.

The powdered metal 46 can be of any suitable composition to form a metal print drum 55 which will have relatively non-wearing print characters on it after the print drum 55 is sintered. One mixture which forms a satisfactory print drum 55 is made of 90% by weight of Ancorsteel 1000 metal powder, one-sixth of which is 150 mesh powder, two-sixths of which is 200 mesh powder and three-sixths of which is 250 mesh powder, and 2% of copper metal powder manufactured by the Alcan Company and having the designation MD103.

In order to isostatically compress the powdered metal 46 against the character sleeve 40 and into character depressions 49 thereof, a precompression pressure of 6 tons per square inch is applied by ram 14 and against the mold l8 and in turn against the ram 16. The pressure on glycerine contained in the pipe 53 is then brought up to 2.8 tons per square inch during a period of about 5 seconds. The pressure on glycerine 48 in pipe 51 is l times this pressure and therefore increases to about 28 tons during a period of seconds. The pressure in pipe 51 is monitored and as the pressure passes about 4 tons, the pressure produced by ram 14 on mold 18 is increased from 6 tons to 30 tons over a period of about 5 seconds. The pressure on the outside of mold 18 produced by ram 14 and against ram 16 is maintained about 2 tons per square inch above the pressure applied to the inside of expandable bag 32 within mold 18. The glycerine 48 in pipe 51 passes upward through bore 22 and through bore holes 47 of support cylinder 28 to cause a pressure of about 28 tons per square inch to be applied through expandable bag 32 against the metal powder 46 and against character sleeve 40. A compacted unsintered metal print drum 55 is thus 4 formed in the apparatus of FIG. 1 in a period of about 5 seconds.

The mold 18 is raised out of enclosure 20 by causing rams 16 and 14 to raise. The support cylinder 26 and sealing ring 34 are removed from the support ring 38 and the top ring 42 is also removed from the support ring 38. The rigid support ring 38 with the unsintered print drum 55 and character sleeve 40 in it is placed in a chuck of a horizontal boring machine and the internal diameter of the metal print drum 55 is made the necessary diameter for mounting on a mounting core. After machining the support ring 38 is inserted in an arbor press and an annular push rod thereof ejects the print drum 55, with the character sleeve 40 around it, from the support ring 38.

The print drum 55 and attached polyurethane character sleeve 40 are heated to between 200 and 250F and the sleeve 40 is cut from the print drum 55. The heating sufficiently softens the polyurethane sleeve 40 so that the characters 56 on the outer periphery of the unsintered print drum 55 which is shown in FIG. 5 are not damaged when the sleeve 40 is removed.

FIG. 2 shows a compressible character sleeve 40 in greater detail. The character depressions 49 of the character sleeve 40 go into the inner surface 58 to a depth such as 0.017 inches, which is about 63% of the wall thickness, such as 0.027 inches, of the character sleeve 40. The use of such a depth increases the strength of print characters 56 of a metal print drum 55 shown in FIG. 5 due to the decrease in the movement of the metal which makes up the print characters 56 during isostatic compression. The character depressions 49 can have any selected pattern in the inner .surface 58 of the character sleeve 40. The outer surface 60 of the character sleeve 40 is made smooth to lie flat against the inner surface of support ring 38 of FIG. 1.

FIG. 3 shows an injection mold 62 which is used to form character sleeve 40. A solid, metal master print cylinder 64, such as a steel master print cylinder, which has raised characters 66 such as 0.017 inch high characters on its outer surface 68, is used to form a pattern of depressions 49 on the inner surface 58 of injection molded character sleeve 40. The character depressions 49 are made to have the same pattern as the printcharacters 56 formed on the metal print drum 55 of FIG. 5. The raised characters 66 on the master cylinder 64 have a height such as 0.017 inches and face width which is about 33% greater than the height :and face width of the print characters 56 which are formed on the metal print drum 55. The character depressions 49 in the character sleeve 40 are therefore about 33% deeper and wider than the height and face width of the print characters 56 formed on the metal print drum 55. This takes into account a compression of the sleeve of about 33 percent during isostatic compaction. As the sleeve 40 compresses, the sleeve wall portion 70 compresses radially and therefore the sidewall of the sleeve wall portion 70 (which also corresponds to the sidewall of the character depression) expands into the character depression so as to exert lateral compacting forces on the powdered metal, thus enhancing the strength of the print character being formed.

The character sleeve 40 can be made from any suitable compressible material such as polyurethane plastic material having Va inch long glass fibers in it to increase its strength. The temperature of the plastic material is raised to 400F. prior to its injection into mold 62. Glass fibers in polyurethane plastic material tend to prevent the character sleeve 40 from shrinking after being molded, and the character depressions 49 tend to maintain better vertical alignment when the glass fibers are used as previously discussed.

The injection pressure of the polyurethane plastic material is about 18,000 pounds per square inch. The temperature of the injection mold 62 is about 160F. After injection the polyurethane plaatic material is cooled to about 120F. by means of a water cooling unit 74 and the top half 76 of injection mold 62 is raised. The warm character sleeve 40 is removed from around the master print cylinder 64 by placing thin shims between the character sleeve 40 and the master print cylinder 64 and then pulling the compressible character sleeve 40 upward over the shims.

FIG. 4 shows how a compressible character sleeve 40 is used to form metal print drum 55 by means of isostatic compression from an expandable bag 32. Raised type characters 56 are formed within the character depressions' 49 within the inner surface 58 of the character sleeve 40. The support cylinder 26 supports the expandable bag 32 and the support ring 38 supports the compressible character sleeve 40. The metal enclosure supports the support ring 38.

As shown in FIG. 5, the print characters 56 have a height of about 0.01 12 inches. The metal print drum 55 has a cylindrical wall 80 whose thickness is approximately one-quarter inch and whose inner diameter has been machined on a horizontal boring machine to about 1 /8 inches prior to sintering of the metal print drum 55. The sintering is done after a mounting core 82 is placed in the metal print drum 55 and the sintering is done at a temperature of 2,050F. in a dissociated ammonia gas atmosphere over a period of time of about minutes. The mounting core 82 is tightly encased by the metal print drum 55 due to the heat of sintering. The characters 56 are brought to a hardness of near Rockwell B80 after sintering. After sintering the mounting core 82 and print drum 55 are steam treated for 1 hour at 900F. to provide corrosion resistance and to further harden the characters 56 to a hardness of Rockwell B80.

The mounting core 82 is isostatically formed by isostatic compression of powdered metal around a central spindle using an outer contracting bag which has powdered metal in it, to form a shaft hole 86. The mounting core 82 can be isostatically formed from powdered metal which is 3% by weight of copper powder, 96% by weight of iron powder and 1% by weight of zinc stearate. The mounting core 82 is hardened by sintering at the same time that the metal print drum 55 is hardened by sintering. The mounting core 82 allows the print drum 55 to be mounted in a printing calculator or other device that requires a cylindrical print drum. A shaft is epoxied into the shaft hole 86 to mount the print drum 6 55. The diamter of the print drum 55 may be changed to satisfy the design requirements of a given printing device.

I claim:

1. Apparatus for making a hollow cylindrical metallic print drum having raised type characters on its outer surface, comprising:

a compressible cylindrical character sleeve having character depressions formed on the inner surface thereof;

rigid die means surrounding said character sleeve;

and

isostatic compaction means for pressing powdered metal against the inner surface of said character sleeve in a radial direction with respect to the sleeve axis and for compressing said powdered metal and said compressible character sleeve against said rigid die means, the side walls of said depressions expanding as said sleeve is compressed so as to exert compacting forces in a direction other than said radial direction upon the powdered metal contained within such depressions.

2. The apparatus as set forth in claim 1 wherein the character depressions have a depth and width greater than the height and width of the raised type characters by an amount equal to the amount of compression of the character sleeve during isostatic compaction.

3. The apparatus as at forth in claim 1 wherein the sleeve is reinforced with a filler material to increase its strength and prevent motion of the character depressions in the axial direction of the sleeve during isostatic compaction.

4. The apparatus as set forth in claim 1 wherein the rigid die means includes a rigid support ring having a cylindrical opening, the surface of which is in contactwith the outer surface of the character sleeve and the height of which is at least equal to the length of the print drum to be formed;

wherein the isostatic compaction means includes an expandable isostatic bag having a lip spaced from the inner surface of the character sleeve within the volume circumscribed by said sleeve;

and

support cylinder for supporting the expandable isostatic bag and the lower surface of its lip and for conveying a pressurized liquid against the inner surface of the expandable bag; and wherein said apparatus further includes a sealing ring below the rigid support ring and interleaved to the top of the lip of the isostatic bag; and

a top ring above the rigid support ring for forming a closed cavity between the character sleeve and the isostatic bag. 

1. Apparatus for making a hollow cylindrical metallic print drum having raised type characters on its outer surface, comprising: a compressible cylindrical character sleeve having character depressions formed on the inner surface thereof; rigid die means surrounding said character sleeve; and isostatic compaction means for pressing powdered metal against the inner surface of said character sleeve in a radial direction with respect to the sleeve axis and for compressing said powdered metal and said compressible character sleeve against said rigid die means, the side walls of said depressions expanding as said sleeve is compressed so as to exert compacting forces in a direction other than said radial direction upon the powdered metal contained within such depressions.
 2. The apparatus as set forth in claim 1 wherein the character depressions have a depth and width greater than the height and width of the raised type characters by an amount equal to the amount of compression of the character sleeve during isostatic compaction.
 3. The apparatus as at forth in claim 1 wherein the sleeve is reinforced with a filler material to increase its strength and prevent motion of the character depressions in the axial direction of the sLeeve during isostatic compaction.
 4. The apparatus as set forth in claim 1 wherein the rigid die means includes a rigid support ring having a cylindrical opening, the surface of which is in contact with the outer surface of the character sleeve and the height of which is at least equal to the length of the print drum to be formed; wherein the isostatic compaction means includes an expandable isostatic bag having a lip spaced from the inner surface of the character sleeve within the volume circumscribed by said sleeve; and a support cylinder for supporting the expandable isostatic bag and the lower surface of its lip and for conveying a pressurized liquid against the inner surface of the expandable bag; and wherein said apparatus further includes a sealing ring below the rigid support ring and interleaved to the top of the lip of the isostatic bag; and a top ring above the rigid support ring for forming a closed cavity between the character sleeve and the isostatic bag. 